Zimbabwe authorities have filed court papers accusing opposition number two Tendai Biti of subverting the government, adding that he faces the death penalty, an AFP journalist saw Thursday.

A police charge sheet filed in court accuses Biti of "subverting a constitutional government as defined in the criminal law."

The accusations including seeking "to render the country ungouvernable including the possibility of resorting to an armed insurrection."

The court file also shows prosecutors opposing bail for Biti since "the accused is facing serious offences which attract capital punishment."

Biti, who has not been officially charged, was arrested Thursday minutes after arriving back in Zimbabwe following a long stay in South Africa and has been held in prison since then.

Police have said they plan to charge him with treason, and his arrest comes just ahead of a June 27 presidential run-off election.

He appeared in court for about 40 minutes on Thursday before the case was delayed for lawyers on both sides to hold discussions.

The court papers list four separate charges, though they do not refer specifically to treason.

Police accuse him in the charge sheet of having "incited and conspired ... to rig" the March 29 first round of the election and of having offered bribes ranging from three billion to 50 billion Zimbabwean dollars.

Soaring inflation in Zimbabwe makes it impossible to estimate how much the currency is now worth, but the official inflation is put at 165,000 %.

The bribery led to "massive election rigging," it says.

Other charges accuse him of "publishing or communicating false statements prejudicial to the state" and "causing disaffection among defence forces."

According to police, he is also accused of "undermining authority or insulting the president" and "projecting the president as an evil man" who should be tried for crimes against humanity.